The present invention relates to Faraday cups, particularly to Faraday cup arrays for monitoring ion beam implantation, and more particularly to an improved Faraday cup array by extending the sensitivity range to below 106 ions/cm2, having an insertable plate in the aperture whereby the aperture area is scaleable to between  less than 1 cm2 to  greater than 750 cm2, and enabling ultra-high vacuum applications.
For ion implanters, a Faraday cup assembly or array is commonly used for determining the dose of ions (i.e., ions/cm2) delivered to a substrate and for monitoring the uniformity of the dose delivered to substrates. Typically, this assembly consists of four Faraday cups located at the corners of the ion beam raster pattern (e.g. square or rectangular) and includes an aperture that allows a central region of the raster pattern to be projected onto the substrate. A commercially available Faraday cup assembly is schematically illustrated in FIG. 1 and described in greater detail hereinafter. The assembly as shown in FIG. 1 includes a movable Faraday flag which allows setup of the implantation conditions while precluding implantation of the wafers or substrates mounted on a research cube. The flag is placed into the implant position to allow the projection of the scanned area onto the wafers or substrates. Prior Faraday cup assemblies or arrays were designed to perform well for ion doses of 1011-1018 ions/cm2. In addition, commercially available Faraday cup assemblies are designed with a single projection aperture size for each assembly. While this is desirable for high-dose implantations, it is not necessary for low-dose implantations. Also, existing Faraday cup assemblies are quite complicated, not easily scaleable to larger aperture areas, and not compatible with ultra-high vacuum (UHV) applications. Thus, there is a need in the art for a structurally simple, easily scaleable Faraday cup assembly or array that is also UHV compatible.
The present invention provides a solution to the above-mentioned need by providing an improved Faraday cup assembly which extends the typical prior sensitivity of from 1011-1018 ions/cm2 down to below 106 ions/cm2; provides for varying the aperture size without changing the positions of the Faraday cups, which are selected for the operation of the largest aperture; enables the aperture area to be easily scaleable between  less than 1 cm2 and  greater than 750 cm2; and incorporates UHV-compatible materials in a versatile mounting structure.
It is an object of the present invention to provide an improved Faraday cup assembly for ion beam implantation applications.
A further object of the invention is to provide a Faraday cup assembly which extends the sensitivity range to be 106 ions/cm2.
A further object of the invention is to provide a Faraday cup assembly having an aperture area scaleable between  less than 1 cm2 to  greater than 750 cm2.
Another object of the invention is to provide an improved Faraday cup assembly for an ion implanter wherein the sensitivity range is extended, the aperture area can be varied, and is constructed of materials compatible with ultra-high vacuum (UHV) applications.
Another object of the invention is to provide an improved Faraday cup assembly for ion implantation which utilized an insertable plate that defines the aperture, whereby the aperture area can be varied by simply changing the insertable plate.
Other objects and advantages of the present invention will become apparent to those skilled in the art from the following description and accompanying drawings. The present invention is a versatile, high sensitivity Faraday cup array or assembly for ion implantation. The assembly of this invention extends the sensitivity of prior assemblies of 1011-1018 ions/cm2, to below 106-1018 ions/cm2 and provides a structurally simple, easily scaleable aperture area of between  less than 1 cm2 and  greater than 750 cm2, and incorporates UHV-compatible materials. The present invention allows for varying the aperture size by changing only an insertable plate that defines the aperture without changing the positions of the Faraday cups, which are selected for the operation of the largest aperture. By a unique design and selection of materials, the present invention extends the sensitivity to below 106 ions/cm2, and enables UHV applications. Thus, the versatile, high sensitivity Faraday cup array or assembly of the present invention can more effectively be utilized for dosimetry and uniformity measurements during ion implantation or electron irradiation of materials.